1. Field of the Invention
The present invention relates to a drive unit of a valve body such as a ball valve, a butterfly valve and the like, and particularly relates to a series (a product group) of valve drive units which can drive the valve body via reduction gears.
2. Description of the Prior Art
A valve unit having a ball valve, a butterfly valve, or the like is generally known. The valve unit is disposed in a pipe of building materials, a sewage drain, for example, to open and close a duct and to adjust the quantity of flow. To drive these valve units, various types of manual or electric valve drive units are suggested. Japanese Patent No. 3054540, for example, discloses a valve drive unit employing a worm gear mechanism which is the most commonly used. In addition to the drive unit with the worm gear mechanism, a drive unit with a simple planetary gear mechanism is suggested to realize space savings.
These drive units have to smoothly rotate the valve body during rotating operation, in order to properly adjust the quantity of fluid flowing through the duct. On the other hand, when the valve body is stopping, the drive units should have function of preventing reverse rotation of the valve body (anti-counter-rotating function), because the fluid flowing through the duct puts a heavy load on the valve body.
When the valve drive unit employs the worm gear mechanism, it is possible to have a high anti-counter-rotating effect because its structure effectively limits the reverse rotation. The drive unit, however, has low rotational efficiency during the rotating operation (especially at a start of rotation,) so that there is a problem that the drive unit needs high power consumption in a case where the drive unit is frequently actuated by a motor.
On the other hand, when employing the simple planetary gear mechanism, the drive unit has higher rotational efficiency as compared with that with the worm gear mechanism. However, there is another problem that the drive unit is weak against the load put on the valve body because of its structure easy to rotate in reverse.